1. Field of the Invention
In general, the present invention relates to a device, system and method for subsea piston accumulators utilized with blowout preventers in oil and gas well operations. More particularly, the present invention provides an improved bladder having a dispersion tube to ensure the hydraulic fluid stored in the bladder is communicated into the seawater chamber of the subsea piston accumulators as desired.
2. Description of the Prior Art
As known in the art, a blowout preventer is a large, specialized valve or similar mechanical device, usually installed redundantly in stacks, used to seal, control and monitor oil and gas wells. Blowout preventers were developed to cope with extreme erratic pressures and uncontrolled flow, often referred to as a formation kick, emanating from a well reservoir during drilling. Kicks can lead to a potentially catastrophic event known as a blowout. In addition to controlling the downhole pressure occurring in the drilled hole and the flow of oil and gas, blowout preventers are intended to prevent tubing such as drill pipe and well casing, tools and drilling fluid from being blown out of the wellbore when a blowout threatens.
A typical subsea deep-water blowout preventer system includes hydraulic accumulators module that maintains the hydraulic fluid pressures needed to actuate valves on the blow out preventer. A subsea accumulator stores hydraulic fluid under pressure and must release the hydraulic fluid on demand to provide fast closure of the preventers and for cycling all critical components. The fluid to be pressurized is typically an oil-based product or a water based product with added lubricity and corrosion protection. Accumulators with a piston typically have a piston sliding up and down a seal bore to separate the fluid from the gas.
It is also known that a depth compensated piston accumulator must maintain a constant working fluid pressure in the working fluid chamber at any depth. At the surface, the nitrogen chamber is charged to a specific pressure, which exerts a force on top of the piston, which in turn pressurizes the working hydraulic fluid on the other side of the piston. As the accumulator is lowered deeper into the ocean, the ambient seawater pressure squeezes the hydraulic fluid in the bladder to the same pressure. This seawater pressure from the bladder is exerted on top of the piston in the seawater chamber. Essentially, all of the pressure force that is lost from the nitrogen due to the increased water pressure in very deep water is regained by directing that ambient pressure to the seawater chamber.
Furthermore, when the working fluid chamber is full with the working fluid, the seawater chamber hydraulic fluid is stored in the bladder. In this situation, the bladder is completely full. When the working fluid is expelled from the working fluid chamber, the seawater chamber is filled with the hydraulic fluid from the bladder. It is desirable that the seawater chamber fill completely, which is a function dependent on the bladder performance.
The bladder must communicate fluid to the seawater chamber as needed as well as receive fluid from the seawater chamber. A known problem is ensuring that the hydraulic fluid is able to get into the seawater chamber from the bladder. As the piston moves and the volume in the seawater chamber increases, the fluid from the bladder is sucked into the seawater chamber. If fluid is not transferred, a vacuum will be pulled into the chamber and the depth compensation function will fail.
It is known that bladders are typically made for a nylon material and also provided with a liner. It is also known in the prior art devices for the liner to collapse inside the bladder when fluid is being sucked into the seawater chamber. This may impede the flow of the fluid and prevent the accumulator from working properly and or as efficiently.
Thus, there is a need for an apparatus, process and or system that provides a functioning bladder system for use with a subsea piston accumulator. It is desirable to fill these needs with reliable technology that are affordable and attractive to accumulator operations associated with blow out preventers. The above discussed limitations in the prior art is not exhaustive. The current invention provides an inexpensive, time saving, more reliable apparatus, method and system bladder functionality where the prior art fails.